Generally, a wide range of commercial goods are packaged in a square-shaped bag with an opening on one side of the bag from which it is possible to remove the contents. The opened bag remains box shaped, and functions as the packaging material until the contents are consumed. On the other hand, a tetrahedral packaging material in which the direction of one side is orthogonal to the direction of the opposite side is known as the so-called tetra-type packaging material (trade name: Tetra Pak).
There are many patent applications related to packaging material, such as the following four applications:    Patent Document 1: Japanese Laid-open Patent Application No. 2005-138899;    Patent Document 2: Japanese Laid-open Patent Application No. 2000-264348;    Patent Document 3: Japanese Laid-open Patent Application No. 2000-153871; and    Patent Document 4: Japanese Laid-open Patent Application No. 9-30559.For example, in Patent Document 1, a food-grade packaging bag is described in which a circuitous part that protrudes upward to a perforated line for unsealing is provided, and the bag can be easily opened by opening the circuitous part to the left and right. In Patent Document 2, a structure is described in which an adhesive material is interposed between the lid and the trunk of the packaging bag assembly to facilitate unsealing.
On the other hand, a tubular packaging material with a backing member having constant width tearing property is described in, e.g., Patent Document 3 as a packaging material that facilitates unsealing, and a packaging material having excellent tearing characteristics is described in Patent Document 4 in which a film having tearing characteristics is sandwiched and laminated by different tearing-type films. However, these packaging materials have the following technical problems.